Non-destructive testing utilizing X-ray diffraction techniques is playing an increasingly important role in measuring residual stresses and other material characteristics. Once limited to laboratory conditions, X-ray diffraction is now made available for use in the field to analyze parts and structures of unlimited size and in almost any location. Advances in the art made possible by the assignee of the present invention allows on-site investigation in practical working environments, that is, in spaces constrained by real world equipment. To this end, open beam-type X-ray diffraction equipment has been employed most effectively. In those systems, the X-ray goniometer head is cantilevered and carries fiberoptic detectors toward the forward end thereof. Nevertheless, in order to meet the demands of industrial manufacturers and others, it has become increasingly important to reduce the size of the X-ray diffraction head, thus placing greater emphasis on cooling requirements.
One class of X-ray generating devices has an X-ray tube mounted within a vacuum housing. The X-ray tube includes anode and cathode assemblies, with the cathode assembly emitting electrons when energized. The anode assembly provides an anode target axially spaced from the cathode and oriented so as to receive streams of electrons emitted by the cathode. The electrons are typically focused at a spot or line on the anode target utilizing high voltage beam-confining fields. The anode target is made of a high refractory metal so that electrons striking the anode material impart kinetic energy sufficient to generate X-rays. The X-rays are passed through a window of the vacuum enclosure and are collimated so as to be directed with sufficient intensity on an object to be tested.
Typically only a small percentage of energy inputted to the X-ray tube results in the production of X-rays. The remaining energy is converted through various processes into high temperature heat within the vacuum tube. For example, certain secondary processes cause internal heating of the X-ray tube components. Back scattering results from electrons bouncing off the anode target so as to impinge upon various components of the X-ray tube located within the evacuated housing. It is essential that high operating temperatures within the X-ray tube be efficiently reduced and that the heat loading of the overall system be effectively dissipated by appropriate cooling equipment.
As mentioned, in one class of X-ray generating devices, an outer housing surrounds the evacuated housing of the X-ray tube. The spacing between the inner evacuated housing and the outer housing provides a cavity which is filled with a heat transfer medium such as air (by default), water or glycol-based fluid. A dielectric gas or liquid fluid medium can also be employed. This cavity is sometimes filled with a special liquid coolant such as dielectric oil or water, which can be circulated so as to transfer heat loading from the evacuated housing, through the outer housing to an appropriate external cooling station. In these applications, the cooling medium also serves as an electrical insulator which must withstand the electrical potential between the inner evacuated housing, typically operated at a high voltage potential and the outer housing typically operated at ground potential. As is becoming increasingly better understood, a number of different processes give rise to particulates and other contamination which become entrained in the cooling medium. Included, for example, is the catalytic formation of oil carbon deposits at local high temperature sites located along the evacuated housing. It is important that the particulates and other contaminants be removed from the coolant medium before they enter regions of high electric field between the inner and outer housings, thus giving rise to the possibility of a high voltage breakdown event.
In another class of X-ray generating device, the X-ray tube is operated in a “dry” environment, with the cavity between the X-ray tube and the outer housing being devoid of a liquid medium. However, because of the high heat loadings encountered, an effective coolant arrangement must be provided for the X-ray tube, especially the anode portion thereof. In one arrangement, a manifold is fixed to the X-ray tube and coolant lines are connected to the manifold. Filtration screens are sometimes provided for the manifold assembly and thus are physically carried by the X-ray tube. Service of these filtration screens requires removal of the X-ray tube from its housing, even though the X-ray tube itself does not require service. Such filtration service procedures create difficulties and can compromise the alignment of the tube relative to the housing, and particularly the tube anode assembly relative to the housing window, and may lead to contamination of the X-ray tube surfaces. With respect to tube/housing alignment, it has been found that unbolting the tube and housing from each other for disassembly and then rebolting the tube and housing together can cause slight variations in the relative positions between the anode assembly and window due to the tolerances between the bolts and apertures therefor potentially leading to inaccuracies in test measurements. Accordingly, ensuring proper tube and housing alignment can create significant servicing overhead in current x-ray heads.